June 06, 2011

Erectus out of Georgia?

The presence of a tool-using population on the edge of Europe so early hints that the northern continent, rather than Africa, may have been the evolutionary birthplace of H. erectus. Unfortunately, the fossils of the hominins responsible for making the tools are not proving very helpful to the debate.

Fossilized bone fragments found in the same sedimentary layers as the Dmanisi artefacts are too weathered to be identified as belonging to any one species, so it is impossible to say for sure whether the tools were made by H. erectus.

Neither do fossil skulls previously retrieved from later sediments at the site help to resolve the controversy. These fossils, dating from 1.77 million years ago, had brains between 600 and 775 cubic centimetres in volume, whereas H. erectus is generally thought to have had an average brain size of around 900 cubic centimetres. For comparison, modern humans have a brain capacity of around 1,350 cubic centimetres. "Many people call those Dmanisi fossils the earliest H. erectus, but there is still frequent debate about this," explains Ferring.

The early Pleistocene colonization of temperate Eurasia by Homo erectus was not only a significant biogeographic event but also a major evolutionary threshold. Dmanisi's rich collection of hominin fossils, revealing a population that was small-brained with both primitive and derived skeletal traits, has been dated to the earliest Upper Matuyama chron (ca. 1.77 Ma). Here we present archaeological and geologic evidence that push back Dmanisi's first occupations to shortly after 1.85 Ma and document repeated use of the site over the last half of the Olduvai subchron, 1.85–1.78 Ma. These discoveries show that the southern Caucasus was occupied repeatedly before Dmanisi's hominin fossil assemblage accumulated, strengthening the probability that this was part of a core area for the colonization of Eurasia. The secure age for Dmanisi's first occupations reveals that Eurasia was probably occupied before Homo erectus appears in the East African fossil record.

6 comments:

"Eurasia was probably occupied before Homo erectus appears in the East African fossil record"

The emphasis should be on record, as in: what has been found, so far.

At any rate, as I have mentioned several times, I believe that during sufficiently wet and mild times, there is no strong genetic boundary between Europe, West Asia, and Africa. I think there are clear signs of co-evolution during late ergaster, antecessor, and heidelbergensis times - so it is not really surprising that this also happened (at least sporadically) during early ergaster/erectus times.

Erectus was clearly quite advanced and must have heavily relied on good hunting skills to be able to occupy much of Europe and Asia in a relatively short time span.

"The presence of a tool-using population on the edge of Europe so early hints that the northern continent, rather than Africa, may have been the evolutionary birthplace of H. erectus".

Makes sense. To me it has always seemed unlikely that H. erectus expanded around much of the world and then separate populations remained fixed and isolated in each region. Backwards and forwards movement around the world has probably been happenning since H. erectus first appeared. And probably for Australopithecus in Africa before that time.

"The secure age for Dmanisi's first occupations reveals that Eurasia was probably occupied before Homo erectus appears in the East African fossil record".

And H. erectus appeared very soon after in SE Asia. And in Africa it became H. ergaster.

"This reaises the question of whether genes from homo species that evolved in Europe were actually responsible through admixture for the emergence of homo sapiens, even if HS evolved mainly in Africa".

"It should not be a surprise that additional regions, with vastly different subsidence challenges, should help".

Yes. The idea that all humans descend from just some small population in just one small region of the earth is preposterous. Inbreeding would rapidly become a major problem without even taking any other problems into consideration.

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